During the course of Release the player discovers the Vex have been conducting behavioural experiments on the Fallen they have taken prisoner, whereby the Vex promise to release the Fallen only if they fight each other to the death. Demonstrating that Fallen hierarchies are bound together by more than just fear of their Captains, Barons and Kells, but are held together with actual and genuine loyalty as well, not a single Fallen attacks one another and they all wait patiently to die of old age, imprisoned by the Vex. So they would remain until the player, at the behest of Failsafe, enters the subterranean prison, murders the Vex, and releases the Fallen, who rather than being grateful attack the guardian, forcing the player to kill them too. Eventually the player proceeds far enough into the caves that Vex Wardens are sent to stop them. The player defeats these, and then learns that the Vex are gathering far more Fallen in more prisons, conducting research and experiments on them for an as yet unknown purpose. Failsafe's decade long imprisonment by the Vex during Hack the Planet, may be the cause of her sympathy with the Fallen captives when she says "imprisonment by the Vex is not a fate I would wish on anyone", and the trauma she experienced during her own captivity, and when witnessing the experiments conducted on the Exodus Black crew, may be why she is so insistent that the player's killing the Fallen is better than their remaining in Vex captivity.

Gameplay

Failsafe (Cheery): Captain. The Vex appear to be capturing Fallen. I have traced a high number of prisoners to a cave near your location. Imprisonment by the Vex is not a fate I would wish on anyone! Perhaps we can help.

Ghost: Failsafe, just so you know, the Fallen probably won't thank us for helping them.

Failsafe (Depressed): Trust me. Either way you'll be doing them a favor.

The player proceeds through the cave before finding their path blocked by a Vex barrier being powered and guarded by a "Minotaur Guard". The player kills the Guard, lowering the barrier and continuing inside.

Ghost: We're in! I've never done a prison break before!

Failsafe (Cheery): Good luck, Captain!

The player enters the room beyond, finding more Minotaur Guards powering more barriers which have been used to contain several squads of Fallen inside, including an "Unyielding Servitor.

Clear the room

Destroy the Vex constructs experimenting on the Fallen.

As each Vex Minotaur is killed, The Fallen it had imprisoned are freed at the same time as more Vex reinforcements arrive, causing a three way battle between the Vex, the Guardian, and the Fallen who are shooting at both. The player kills all the Vex and all the Fallen and advances deeper into the Mists.

Ghost: There sure are a lot of Fallen down here. I'm picking up barriers ahead, and below us. Deep below us.

Failsafe (Cheery): Captain, that could mean more prisoners! You should free them!

Ghost: Failsafe, they tried to kill us.

Failsafe (Depressed): Better that than dying in a cage.

Head deeper into the cave

Track the Vex research deeper into the complex

The player enters another room with more captive Fallen being held by more Minotaur Guards.

Ghost: "I think they're running a test to see if they can get this thing to self-replicate. And failing, thank goodness. If the Vex were able to manipulate matter THAT easily, we'd be in a lot more trouble."

The player kill the Guards and the Vex reinforcements, along with the Fallen after the now liberated Fallen attack them.

Ghost: All clear! Not a single Vex, or Fallen in sight. I'm sorry it had to end this way, Failsafe.

Failsafe (Cheery): The attempt was appreciated, friendly Ghost.

The player continues further into the cave, encountering an object of some kind in the center of a small room between two giant Minotaur statues.

Examine Vex relic

The Vex relic may contain useful information.

Interact

Ghost: They've taken - wow - a lot of Fallen. This is just the tip of the facility. This group was told they could "terminate each other" and the survivor would be set free. None of them fired a shot. Except at us, I mean. Gotta admire that loyalty.

As a reward for completing this adventure, the player receives the Unethical Experiments Mark, Cloak, or Bond depending on their class, reading:

"I've seen experiments like this before. My crew.... I don't want to talk about it." — Failsafe

The title of the Minotaur bosses at the end of this Adventure, "Vex Warden" is the same as the Hydra boss at the end of Lost Crew, which together with the experiments described during the two adventures and the Unethical Experiments class item suggests a commonality between them